Heart cell death during ischemia or hypoxia following myocardial infarct may result from an extreme lowering of the free adenine ribonucleotide content within the heart cells. Leakage of purine bases and nucleosides has been documented and changes in the maintenance patterns are apparent during these stresses or during recovery from these stresses. The metabolic pattern for normal stabilization of the adenine ribonucleotide pool and the changes which occur with ischemia are the subject of the proposed investigation. The investigation will employ a series of 15N tracer studies in combination with enzymological investigations. Primary concern is focused on the N-6 vs purine ring N differential enrichment in the purfused rat heart preparations. Procedures involve extraction of the nucleotides, separation by high pressure liquid chromatography, and derivitization and analysis by gas chromatography-mass spectrometry. The method is fast and requires only micrograms of material for complete analysis. These investigations in combination with studies on changes in the amino acid pool sizes in the heart tissues to evaluate isotope dilution and concentration effects, will provide direct information on the mechanisms regulating the adenine nucleotide pool size. These studies can be extended to tumor cells, arthritic disease states, etc. and to the effects of specific pharmacological agents which might interfere with adenine nucleotide and purine metabolism.